In an exhaust system for a motorcycle, it is required to exhibit sufficient silencing effect to reduce noise. For example, Japanese Laid-Open Patent Application Publication No. 2006-307793 describes an exhaust system capable of enhancing the silencing effect. According to this conventional exhaust system, an outer cylinder and an inner cylinder constituting a muffler are gradually tapered rearward of a vehicle body, and a cross sectional area ratio of the inner and outer cylinders is substantially constant in the front/rear direction.
In the case of the conventional exhaust system, although the silencing effect can be enhanced, there is a problem that the engine output is reduced as the silencing effect is enhanced.